1. Field of the Invention
The present invention relates to a brake for a bending control device of an endoscope and, more particularly, to a brake for an endoscope bending control device of the type wherein a driver that pulls a bending control wire is braked by means of frictional force to maintain the bendable portion of the endoscope in a desired bent state.
2. Description of the Related Art
The bending control device of an endoscope includes a brake which is used to maintain the bendable portion of the endoscope in a desired bent state in order to fix the observation field of view. One type of conventional brake for endoscope bending control devices has heretofore been designed to fix the bendable portion in a desired bent position.
However, not considerably inconvenient if it is impossible to vary the angle of bending of the bendable portion after it has been fixed in a particular bent position. Therefore, it is common practice to employ brakes of the type wherein a driver that pulls a bending control wire is braked by means of frictional force so that it is possible not only to maintain the bendable portion in a desired bent state but also to vary the angle of bending after it has been fixed in a particular bent position.
A typical conventional brake of the type described above has heretofore been arranged such that a rotary disk having a plastic or cork material attached thereto is pressed against a fixed disk to produce frictional force to thereby maintain the bendable portion in a desired bent state.
This type of conventional brake suffers, however, from the disadvantage that the diameter of the disks must be increased in order to obtain large frictional force and this leads to an increase in the size of the control part, so that the operability is deteriorated and the mechanism is complicated.
In the bending control devices of endoscopes, the greater the angle of bending of the bendable portion, the greater the resilient force acting on the bendable portion, that is, the greater the force acting on the bendable portion trying to restore it to its straight position. However, the conventional brake structure, having a rotary disk merely pressed against a fixed disk, has no consideration for the relationship between the level of frictional force produced and the magnitude of bending angle. Therefore, if the frictional force is set at a level which will be convenient for the operation, when the bendable portion is bent at a relatively great angle, the frictional force produced cannot resist the resilient force acting on the bendable portion, thus causing the bendable portion to be undesirably restored to its straight position.
If the frictional force of the conventional brake structure is increased so that the bendable portion, when bent at a relatively great angle, will not undesirably be restored to its straight position, the level of frictional force will be excessively high when the bendable portion is close to its straight position. Thus, it will be impossible to conduct smoothly the operation of varying the angle of bending.